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Property management fee percentage.

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Face (par) amount of debt instrument at time of issuance.

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Net increase or decrease in the carrying amount of the debt instrument for the period.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Weighted average interest rate of debt outstanding.

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Debt (Secured Tower Revenue Securities) (Narrative) (Details)									12 Months Ended
	Mar. 09, 2018 USD ($)	Apr. 17, 2017 USD ($)	Jul. 15, 2016 USD ($)	Jul. 07, 2016 USD ($)	Oct. 14, 2015 USD ($)	Oct. 15, 2014 USD ($)	Apr. 18, 2013 USD ($)	Aug. 09, 2012 USD ($)	Dec. 31, 2018 USD ($) site	Dec. 31, 2017 USD ($)	Apr. 16, 2010 USD ($)
Debt Instrument [Line Items]
Debt instrument, principal balance									$ 10,028,000,000	$ 9,405,000,000
Tower Securities [Member]
Debt Instrument [Line Items]
Aggregate number of tower sites owned by Borrowers \| site									10,426
Property management fee percentage									4.50%
U.S. Treasury rate term									10 years
Interest added to Treasury rate and credit-based spread for non-compliance									5.00%
2010-2C Tower Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount											$ 550,000,000
Debt instrument, interest rate, stated percentage											5.101%
Repayment date of debt instrument									Apr. 11, 2017
Debt instrument, maturity date									Apr. 09, 2042
Financing fees											$ 8,100,000
Write-off of deferred financing fees			$ 1,000,000
2012 Tower Securities [Member]
Debt Instrument [Line Items]
No prepayment consideration period									12 months
2012-1C Tower Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount								$ 610,000,000
Debt instrument, interest rate, stated percentage								2.933%
Repayment date of debt instrument								Dec. 11, 2017
Debt instrument, maturity date								Dec. 09, 2042
Write-off of deferred financing fees		$ 2,000,000
Repayments of long-term debt		610,000,000
2013 Tower Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount							$ 1,330,000,000
Financing fees							$ 25,500,000
Debt instrument, weighted average interest rate							3.218%
2013-1C Tower Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount							$ 425,000,000
Debt instrument, interest rate, stated percentage							2.24%
Repayment date of debt instrument							Apr. 10, 2018
Debt instrument, maturity date							Apr. 09, 2043		Apr. 10, 2018
Repayments of long-term debt	$ 425,000,000
Debt instrument, principal balance										425,000,000
2013-2C Tower Securities [Member]
Debt Instrument [Line Items]
No prepayment consideration period									18 months
Debt instrument, face amount							$ 575,000,000
Debt instrument, interest rate, stated percentage							3.722%
Repayment date of debt instrument							Apr. 11, 2023
Debt instrument, maturity date							Apr. 09, 2048		Apr. 11, 2023
Debt instrument, principal balance									$ 575,000,000	575,000,000
2013-1D Tower Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount							$ 330,000,000
Debt instrument, interest rate, stated percentage							3.598%
Repayment date of debt instrument							Apr. 10, 2018
Debt instrument, maturity date							Apr. 09, 2043		Apr. 10, 2018
Repayments of long-term debt	330,000,000
Debt instrument, principal balance										330,000,000
2014 Tower Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount						$ 1,540,000,000
Financing fees						$ 22,500,000
Debt instrument, weighted average interest rate						3.289%
2014-1C Tower Securities [Member]
Debt Instrument [Line Items]
No prepayment consideration period									12 months
Debt instrument, face amount						$ 920,000,000
Debt instrument, interest rate, stated percentage						2.898%
Repayment date of debt instrument						Oct. 08, 2019
Debt instrument, maturity date						Oct. 11, 2044			Oct. 08, 2019
Debt instrument, principal balance									$ 920,000,000	920,000,000
2014-2C Tower Securities [Member]
Debt Instrument [Line Items]
No prepayment consideration period									18 months
Debt instrument, face amount						$ 620,000,000
Debt instrument, interest rate, stated percentage						3.869%
Repayment date of debt instrument						Oct. 08, 2024
Debt instrument, maturity date						Oct. 08, 2049			Oct. 08, 2024
Debt instrument, principal balance									$ 620,000,000	620,000,000
2015-1C Tower Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount					$ 500,000,000
Debt instrument, interest rate, stated percentage					3.156%
Repayment date of debt instrument					Oct. 08, 2020
Debt instrument, maturity date					Oct. 10, 2045				Oct. 08, 2020
Financing fees					$ 11,200,000
Debt service coverage ratio									2
Debt instrument, principal balance									$ 500,000,000	500,000,000
2016-1C Tower Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 700,000,000
Debt instrument, interest rate, stated percentage				2.877%
Repayment date of debt instrument				Jul. 09, 2021
Debt instrument, maturity date				Jul. 10, 2046					Jul. 09, 2021
Financing fees				$ 9,500,000
Debt instrument, principal balance									$ 700,000,000	700,000,000
2017-1C Tower Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		$ 760,000,000
Debt instrument, interest rate, stated percentage		3.168%
Repayment date of debt instrument		Apr. 11, 2022
Debt instrument, maturity date		Apr. 09, 2047							Apr. 11, 2022
Financing fees		$ 10,200,000
Debt instrument, principal balance									$ 760,000,000	$ 760,000,000
2017-1R Tower Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		$ 40,000,000
Debt instrument, interest rate, stated percentage		4.459%
Repayment date of debt instrument		Apr. 11, 2022
Debt instrument, maturity date		Apr. 09, 2047
2018-1C Tower Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 640,000,000
Debt instrument, interest rate, stated percentage	3.448%
Repayment date of debt instrument	Mar. 09, 2023
Debt instrument, maturity date	Mar. 09, 2048								Mar. 09, 2023
Financing fees	$ 8,500,000
Debt instrument, principal balance									$ 640,000,000
2018-1R Tower Securities [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 33,700,000
Debt instrument, interest rate, stated percentage	4.949%
Repayment date of debt instrument	Mar. 09, 2023
Debt instrument, maturity date	Mar. 09, 2048
Mortgage Loan [Member]
Debt Instrument [Line Items]
Debt instrument, increase	$ 673,700,000
Debt instrument, decrease after giving effect to prepayment of loan components	81,300,000
Debt instrument, increase in outstanding principle amount	640,000,000
Debt instrument, principal balance	$ 4,700,000,000
Minimum [Member] \| Tower Securities [Member]
Debt Instrument [Line Items]
Additional interest rate for non-compliance									5.00%
Excess Cash Flow Reserve [Member] \| Minimum [Member] \| Tower Securities [Member]
Debt Instrument [Line Items]
Debt service coverage ratio									1.30
Amortization Period Prepay [Member] \| Maximum [Member] \| Tower Securities [Member]
Debt Instrument [Line Items]
Debt service coverage ratio									1.15